MS-DOS games often received patches to fix bugs, and cracks to disable copy protection. These usually come as sets of files that replace some of the original game’s files. To apply a patch or crack to a game:
If the patch came with its own updater program (called “PATCH.EXE” or similar), double-click on the program to run it and apply the update.
If the program extracts more files of its own, check if they include another updater program: if so, run that too in the same way.